Ridge lasers are routinely used to fabricate single lateral mode index guided lasers. A typical structure of this type is described in U.S. Pat. No. 5,059,552 to C. S. Harder, and of common assignee. Ridge lasers, however, have the distinct disadvantage of having large topologies (i.e., large differences in height between neighboring elements), which makes them difficult to fabricate and expensive to manufacture.
Ridge lasers have an additional disadvantage in that their topology causes a variation in the stress observed in the waveguiding region. This stress is caused by the dielectric and metallization layers--layers that are necessary to form the structure. This can result in difficulties in obtaining a well-confined single lateral mode waveguiding action.
GaAs and AlGaAs semiconductor laser structures have been used successfully to fabricate quantum wells (QWs). Recent developments have shown that a selective intermixing through the use of a SiO.sub.2 cap can substantially increase the bandgap of the QW. This technique is described in the article: "Spatially selective modification of GaAs/AlGaAs quantum wells by SiO.sub.2 capping and rapid thermal annealing" by J. Y. Chi, et al., published in the Appl. Phys. Lett. 55 (9), of Aug. 28, 1989, and has been successfully used to modify the bandgap profile of QWs.
Cleaving a semiconductor laser crystal has been advantageously used to form the facets of a laser. However, for mass fabrication and monolithic integration, it is desirable to use a relatively recent method, namely, forming etched facets through the use of a chemically assisted ion beam etching technique, which has been successfully used in achieving results of similar quality to that of cleaved facets. In the article: "Rectangular and L-shaped GaAs/AlGaAs lasers with very high quality etched facets", by A. Behfar-Rad, et al., published in the Appl. Phys. Lett. 54 (6), of Feb. 6, 1989, a process based on a SiO.sub.2 etch mask is described, which has led to very smooth etched facets.
High power single lateral mode semiconductor lasers have found their way in a variety of applications that range from optical storage, Erbium-doped fiber amplification, and frequency doubling. Reliability considerations show that it is advantageous to have non-absorbing mirrors or facets for semiconductor lasers and especially for high-power semiconductor lasers.
Moreover, current confinement is also desirable to lower the threshold current density since it leads to a lower operating temperature for the semiconductor laser and, hence, further improves its overall reliability. Current confinement also avoids the problem of surface recombination current at the facets. Lateral current confinement within the structure has a further advantage in that it prevents current flow in regions adjacent to the waveguide, thereby making the device less susceptible to the occurrence of non-fundamental modes at high power.
Low vertical far-field (VFF) performance of the laser beam is highly desirable in many applications. A recent article in the article "A periodic index separate confinement heterostructure quantum well laser" by M. C. Wu, et al, Applied Physics Letters 59 (9), Aug. 26, 1991, shows the level of complexity that has been incorporated into the laser structure to achieve low VFF.